1. Field of the Invention
The present invention relates to a gear assembly for transmitting rotation between two shafts. More particularly, it relates to a construction for ensuring the lubrication of such a gear assembly.
2. Description of the Related Art
In a double overhead camshaft (DOHC) engine, two camshafts, located above a cylinder head, are provided with cams opening and closing intake and exhaust valves, respectively. The two camshafts are provided with gears which are in constant mesh with each other, and thus the camshafts are rotated synchronously so that the intake and exhaust valves are opened and closed at a predetermined timing.
In a conventional DOHC engine, a means for supplying lubricating oil to the gears is constructed in such a manner that the oil is supplied to a portion of the gears at which the teeth of the gears are actually in mesh, in a direction along the axis of the shafts. If the supply means is constructed in such a manner that the oil is supplied to the meshing portion in a rotational direction of the shafts, the oil is spread relatively effectively in the meshing portion. However, the supply means cannot be always provided in the farther side of the rotational direction of the gears because of the construction of a head cover mounted on the cylinder head. Therefore, the supply means must be situated at one side of the meshing portion. As a result, lubricating oil discharged from the supply means collides with a side surface of the gears and a certain proportion of the oil is not supplied into the meshing portion but is diverted into the valve mechanism and seeps into the valves. Accordingly, the supply means must supply an increased quantity of oil to the gears. Thus, if the quantity of oil diverted by collision with the side of the gear is increased, the quantity of oil seeping into a PCV valve provided between a crankcase and an intake manifold is increased, so that not only does the exhaust gas emission become worse, but also the oil consumption becomes higher. Further, a large capacity oil pump must be provided to prevent oil pressure at other portions of the head cover from dropping.